PREDICTING HUMAN NOCTURNAL NONVISUAL RESPONSES TO MONOCHROMATIC AND POLYCHROMATIC LIGHT WITH A MELANOPSIN PHOTOSENSITIVITY FUNCTION

Abstract

The short-wavelength (blue) light sensitivity of human circadian, neurobehavioral, neuroendocrine, and neurophysiological responses is attributed to melanopsin. Whether melanopsin is the sole factor in determining the efficacy of a polychromatic light source in driving nonvisual responses, however, remains to be established. Monochromatic (λ_max 437, 479, and 532 nm administered singly and in combination with 479 nm light) and polychromatic (color temperature: 4000 K and 17000 K) light stimuli were photon matched for their predicted ability to stimulate melanopsin, and their capacity to affect nocturnal melatonin levels, auditory reaction time, and subjective alertness and mood was assessed. Young, healthy male participants aged 18–35 yrs (23.6 ± 3.6 yrs [mean ± SD]; n = 12) participated in 12 overnight sessions that included an individually timed 30-min nocturnal light stimulus on the rising limb of the melatonin profile. At regular intervals before, during, and after the light stimulus, subjective mood and alertness were verbally assessed, blood samples were taken for analysis of plasma melatonin levels, and an auditory reaction time task (psychomotor vigilance task; PVT) was performed. Proc GLM (general linear model) repeated-measures ANOVA (analysis of variance) revealed significantly lower melatonin suppression with the polychromatic light conditions (4000 and 17000 K) compared to the “melanopsin photon-matched” monochromatic light conditions (p < .05). In contrast, subjective alertness was significantly lower under the 479 nm monochromatic light condition compared to the 437 and 532 nm monochromatic and both polychromatic light conditions. The alerting responses more reflected the total photon content of the light stimulus. The demonstration that the melatonin suppression response to polychromatic light was significantly lower than predicted by the melanopsin photosensitivity function suggests this function is not the sole consideration when trying to predict the efficacy of broadband lighting. The different spectral sensitivity of subjective alertness and melatonin suppression responses may imply a differential involvement of the cone photopigments. An analysis of the photon densities in specific wavelength bands for the polychromatic lights used in this and the authors' previous study suggests the spectral composition of a polychromatic light source, and particularly the very short-wavelength content, may be critical in determining response magnitude for the neuroendocrine and neurobehavioral effects of nocturnal light. (Author correspondence: [email protected])

Keywords:

• Human
• Light
• Melanopsin
• Monochromatic light
• Polychromatic light

ACKNOWLEDGMENTS

The authors would like to thank Katrin Ackermann, Katharina Lederle, Benita Middleton, Tracey Sletten, Ivonne Vogt, and Sophie Wehrens for their contribution to this work. The authors are very grateful to Peter Williams for statistical advice. This study was supported by Philips Lighting and was carried out as part of a collaborative research agreement between the University of Surrey and Philips Lighting (Eindhoven, The Netherlands). In addition, the authors are grateful to Stockgrand Ltd. for providing radioimmunoassay agents. V.L.R., D.B., and D.J.S. are supported by the 6th Framework project EUCLOCK (018741).